Using a particle image velocimetry, the instantaneous and time average flow fields in the downstream of a wind turbine with a brimmed diffuser are investigated. The time dependent velocity fields are shown by the animation. Furthermore the time average flow velocity vectors are made on an average of the instantaneous velocity data. There are two vortices in the downstream of the wind turbine. One is unsteady vortex near behind the brim, and another is a large blockage vortex in the downstream flow field of the wind turbine. The large blockage vortex is not clear in the instantaneous flow vector animation, however it exists clearly in the time average flow field.